OSI Layer Model

 Data Encapsulation

When the OUM’s student is trying to access the OnlineLearning system located in the OUM network facilities using modem connection, the underlying operating system in the student’s computer will transform the request into data or payload. Since the data is made at the Application Layer which is the Layer 7 of OSI Layer Model, specified protocol of formatting the data will be used. Assumed that the student is accessing the OnlineLearning system through a web browser, HTTP requests will be made. The process of encapsulation will take place so that the Application Layer places a header field that contains information such as fonts and screen size and then passes the data to the Presentation Layer which is Layer 6 of OSI Layer Model. 

    When the data which can be referred as protocol data unit (PDU) on the Application Layer is sent to the next layer, the Presentation Layer will provide a mapping of different syntax which is data will be translated between application and network format so that the two systems come on the same platform for communication and easy to understand each other. Data encryption and compression will also be performed in the Presentation Layer at the sender’s end before transmitting. Then, the Presentation Layer will placed its header information, for example different formats of data such as HTML files, image files and text in a message to be converted to ASCII and later pass the new data to Session Layer which is Layer 5 of OSI Layer Model. 

    The Session Layer controls the connections between two ends by establishing, managing and terminating sessions. When the student requests to access OnlineLearning web page, the web browser opens a TCP/UDP connection which can be referred as session to the web server to wait for the web server to send back to the web page and closes the connection. This layer also provides synchronization in the dialogue between two systems so that the data can be delivered efficiently without any loss. The Session Layer will then follow the same process by adding its layer information such as the data flow that has been managed by the layer and passes the data to the Transport Layer which is Layer 4 of OSI Layer Model.

    In Transport Layer, it is responsible for delivery of a message from one process to another by ensuring an end-to-end error-free connection between the two different hosts. The PDU from the upper layer will be split into smaller pieces called segments if TCP is used as the Transport protocol or datagram if UDP is used instead and then dispenses it to Network Layer for further delivery to the destination host by adding its layer’s information such as an acknowledgement that the segment was received in the header.

    At the Network Layer, it is responsible to accomplish the routing of data packets from the source to destination host between the inter and intra networks operating on the same or different protocols. This layer performs the exchange of data by using a logical network addressing and subnetting designs of the network. By using the logical Internet Protocol (IP) addressing and routers for communication, the packets can be routed from the source to destination despite of the two different networks working on the same or different protocol. The role of the router in this layer is to transmit the data packets between the networks and creates a boundary between two networks as the student’s network and server’s network are not directly connected. The Network Layer will encapsulate the data with source and destination IP address, then determine the best delivery path to the actual host that should receive the data which is the IT Center where OnlineLearning System server is located and send the entire packets to Data Link Layer.

    The second layer of OSI Layer Model which is Data Link Layer is responsible for taking packets from the Network Layer and placing them by 1’s and 0’s on the network medium which is cable. The WiFi Network Interface Card (NIC) in this layer works as transmitting radio waves by interpreting the PDU as a series of 1’s and 0’s. The Data Link Layer will then encapsulate each packet in a frame which contains the Medium Access Control (MAC) address of the source and destination computer and the Logical Link Control (LLC) information which acts as an interface between MAC and network layer. Also, the header and trailer information of layer 2 such as Frame Check Sequence (FCS) which is used for error checking is also added and then passes to the Physical Layer for transmission across the media.

    Since the data has to be sent across the media, which is wireless network in this case as the server is on a remote network, the Physical Layer in the OSI Layer Model will encapsulate 1’s and 0’s as a frame is a logical group of 1’s and 0’s and then the bits are transferred in the form of radio waves. This layer will also ensure the synchronization of bits so that the end user data is assembled in the correct order.

 Data Decapsulation

After the bits are transferred through the network media, the process of data decapsulation takes place which refers to process in which protocol information is removed from the data when it passes through layers. The protocol information are the header and trailers. The process of decapsulation occurs in the opposite direction and flow of the encapsulation process. Therefore, it begins with the Layer 1, Physical. 

     The digital signals of 1’s and 0’s will firstly be synchronized by the recipient computer. Once the synchronization has completed and it successfully receives the whole frame, the bits that are now in frame data unit is passed to the next upper layer. 

     Layer 2 is Data Link layer which is responsible for interfacing with the physical layer. The data link layer examines the frame check sequence (FCS) in the trailer to detect if there is any error. If there is an error, the frame would be discarded. The layer will only read the rest of the frame if it is in correct shape, and then reads the destination address to determine if it is intended for the following process. If it is intended, the header and trailer will be removed from the frame, which then would be known as packets. The following layer would be Network Layer whereby the packets are handed over to.

     The network layer is responsible for packet delivery from end to end. The network layer inspects the destination software address located in the packet’s header. If the IP address that is checked matches the own IP address of recipient, the header is removed from the packet and the rest is passed to the next above layer, Transport Layer. Once the header of packet is removed, it will now be known a segment.

    The segment is sent by the network layer to the transport layer. In this layer, all necessary information is collected from the segment header. According to the information, the segment would be arranged into the correct order. After that, the segment header would be removed from all the segments as it resembles them in original data stream. The data stream will then be handed over to the upper layer, Session Layer. The upper layers format the data stream in form as that the target application can understand.

     In this case, in the session layer, when the webpage is requested, the web browser opens a TCP/UDP connection to the web server, in this case, the Online Learning System server. The web page is sent by the web server before it closes the connection. Each TCP/UDP connection is a session.

    This is the explanation on how data travels from the student’s computer to reach the Online Learning System server related to the OSI Layer Model.

Figure shows the encapsulation and decapsulation process in the OSI model.

Possible Network Components

    The network category involved such as Local Area Network (LAN) as it only interconnects devices within a small, limited area. For instance, in this case it covers the student’s home network and OUM campus network. On the other hand, the public network is categorized as the Wide Area Network (WAN). The network ranges across a large geographical area therefore able to maintain connection between LANs network across cities and countries. It is managed by the Internet Service Provider (ISP) which differs based on its own regional area.

     In terms of network connection, it's a Client-Server. For instance, the student’s computer acts as a client requesting to access content of the OnlineLearning website and the server responsible, located in the IT Center building of OUM Campus, responds by providing associated data. Possible end devices participate in the network connection such as computers, Web Server and Database Server which host the web pages and store data requests from the browser of the student's computer. 

    Apart from that, one of the connecting devices includes a modem which connects the home network to the public network. As modem is only able to connect one device at a time and not able to host Wi-Fi, another possible network component includes a router. It's able to connect student's computer wirelessly to the Internet. The possible network media that connects modem to the router is Ethernet cable such as Unshielded Twisted Pair (UTP) which the category can vary based on the transmission speed and its bandwidth. For instance, Category 5 UTP cable able to support transmission speed up to 100 Mbps while Cat-5e which is the enhanced version of Category 5 able to support up to 1Gbps. The UTP cable also comes with its RJ45 connectors.

    Router also able to run firewalls and connect different network environments such as WAN and LAN. In this case, between the OUM Campus to the wider range of network, the Internet. Based on the OSI Layer Model router works in the Layer 3, Network Layer. Therefore, it acts as the network gateway and route data from one network to another based on the IP address. Another possible network device includes Switch which connects all the devices andexchanges data within a single network which is the OUM Campus Network. Switches work in Layer 2, Data Link Layer which keeps record of MAC addresses of devices connected to it. 

    Another possible transmission media that can be used in this networking is a coaxial cable. The coaxial cable is commonly used by telecommunication companies and internet providers to transmit data such as text, audio, and video. This cable is widely used in homes. It can be used by Internet Services Providers (ISP) to provide the service for customers/users. There are several sizes of coaxial cable. For example, RG-6, RG-11, and RG-59. Every size has its own function. The coaxial cable for the internet is RG-6. It has a larger conductor and provides the better quality of signal. Next, the other possible transmission media is a fiber optic cable that contains glass fiber inside it. The fiber optic cable can transmit more data for a longer distance and provides better performance than the wired cables. Other than that, the fiber optic cable can support the higher bandwidth and provide connectivity for most of the world’s internet. Besides that, there are several wireless transmission media such as radio waves, microwaves and infrared. The suitable wireless transmission media for this networking is microwaves. The microwaves have a high frequency of radio waves to provide the highest speed of wireless connection. The microwaves links are used for point-to-point communication in satellite communication and radio communication because of the small wavelength. It needs the antenna dish and horn dish to connect the connection between networks.

Figure shows a network diagram.